1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  NMI backtrace support
  4 *
  5 * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
  6 * with the following header:
  7 *
  8 *  HW NMI watchdog support
  9 *
 10 *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
 11 *
 12 *  Arch specific calls to support NMI watchdog
 13 *
 14 *  Bits copied from original nmi.c file
 15 */
 16#include <linux/cpumask.h>
 17#include <linux/delay.h>
 18#include <linux/kprobes.h>
 19#include <linux/nmi.h>
 20#include <linux/cpu.h>
 21#include <linux/sched/debug.h>
 22
 23#ifdef arch_trigger_cpumask_backtrace
 24/* For reliability, we're prepared to waste bits here. */
 25static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
 26
 27/* "in progress" flag of arch_trigger_cpumask_backtrace */
 28static unsigned long backtrace_flag;
 29
 30/*
 31 * When raise() is called it will be passed a pointer to the
 32 * backtrace_mask. Architectures that call nmi_cpu_backtrace()
 33 * directly from their raise() functions may rely on the mask
 34 * they are passed being updated as a side effect of this call.
 35 */
 36void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
 37				   int exclude_cpu,
 38				   void (*raise)(cpumask_t *mask))
 39{
 40	int i, this_cpu = get_cpu();
 41
 42	if (test_and_set_bit(0, &backtrace_flag)) {
 43		/*
 44		 * If there is already a trigger_all_cpu_backtrace() in progress
 45		 * (backtrace_flag == 1), don't output double cpu dump infos.
 46		 */
 47		put_cpu();
 48		return;
 49	}
 50
 51	cpumask_copy(to_cpumask(backtrace_mask), mask);
 52	if (exclude_cpu != -1)
 53		cpumask_clear_cpu(exclude_cpu, to_cpumask(backtrace_mask));
 54
 55	/*
 56	 * Don't try to send an NMI to this cpu; it may work on some
 57	 * architectures, but on others it may not, and we'll get
 58	 * information at least as useful just by doing a dump_stack() here.
 59	 * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
 60	 */
 61	if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
 62		nmi_cpu_backtrace(NULL);
 63
 64	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
 65		pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
 66			this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
 67		nmi_backtrace_stall_snap(to_cpumask(backtrace_mask));
 68		raise(to_cpumask(backtrace_mask));
 69	}
 70
 71	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
 72	for (i = 0; i < 10 * 1000; i++) {
 73		if (cpumask_empty(to_cpumask(backtrace_mask)))
 74			break;
 75		mdelay(1);
 76		touch_softlockup_watchdog();
 77	}
 78	nmi_backtrace_stall_check(to_cpumask(backtrace_mask));
 79
 80	/*
 81	 * Force flush any remote buffers that might be stuck in IRQ context
 82	 * and therefore could not run their irq_work.
 83	 */
 84	printk_trigger_flush();
 85
 86	clear_bit_unlock(0, &backtrace_flag);
 87	put_cpu();
 88}
 89
 90// Dump stacks even for idle CPUs.
 91static bool backtrace_idle;
 92module_param(backtrace_idle, bool, 0644);
 93
 94bool nmi_cpu_backtrace(struct pt_regs *regs)
 95{
 96	int cpu = smp_processor_id();
 97	unsigned long flags;
 98
 99	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
100		/*
101		 * Allow nested NMI backtraces while serializing
102		 * against other CPUs.
103		 */
104		printk_cpu_sync_get_irqsave(flags);
105		if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
106			pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
107				cpu, (void *)instruction_pointer(regs));
108		} else {
109			pr_warn("NMI backtrace for cpu %d\n", cpu);
110			if (regs)
111				show_regs(regs);
112			else
113				dump_stack();
114		}
115		printk_cpu_sync_put_irqrestore(flags);
116		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
117		return true;
118	}
119
120	return false;
121}
122NOKPROBE_SYMBOL(nmi_cpu_backtrace);
123#endif